V. A. Shiva Ayyadurai, Dr. E-Mail: Inventor of Email, History of Email, Free EMail Tips

Do not send multi-megapixel sized images weighing in tens of megabytes as this will only lead to the E-Mail server getting overloaded. Try to keep images to sensible proportions. E-Mail is not a high-resolution medium and you do not require anything more than 640 to 800 pixels width for an image to look good in E-Mail.

If you do need to send high-resolution images (maybe for printing), just compress them using ZIP or RAR formats to make them more portable and easy to handle.